Question

嗨我有两个谓词。我想知道是否有可能将它们以某种方式加入到一起？第一：

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.AgentName.ToLower().StartsWith(agentName.ToLower());
};

第二

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
};

这就是联接谓词的样子。

Predicate<object> viewFilter = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower()) && u.AgentName.ToLower().StartsWith(agentName.ToLower());
};

我需要这个用于WPF数据网格过滤器，其中网格源是ICollectionView。因此，在我创建了我的谓词之后，我将其设置为过滤器，如下所示：

private void FilterByLogin(ICollectionView view, string login)
{
    Predicate<object> viewFilter = f =>
    {
        ExternalUser u = f as ExternalUser;
        return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
    };
    view.Filter = viewFilter;
}

Answer 1

我会创建两个新方法：

public static Prediate<object> Cast<T>(Predicate<T> inner)
{
    return new Predicate<object>(o => inner((T)o));
}

public static Predicate<T> And<T>(Predicate<T> p1, Predicate<T> p2)
{
    return x => p1(x) && p2(x);
}

然后你可以从谓词中删除强制转换并将其移到顶层：

Predicate<ExternalUser> first = u => u.AgentName.ToLower().StartsWith(agentName.ToLower());
Predicate<ExternalUser> second = u => u.ExternalLogin.ToLower().StartsWith(login.ToLower());

view.Filter = Cast(And(first, second));

Answer 2

真的应该这么简单：

Predicate<object> viewFilter1 = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.AgentName.ToLower().StartsWith(agentName.ToLower());
};

Predicate<object> viewFilter2 = f =>
{
    ExternalUser u = f as ExternalUser;
    return u.ExternalLogin.ToLower().StartsWith(login.ToLower());
};

Predicate<object> viewFilter = f => viewFilter1(f) && viewFilter2(f);

如何组合c＃谓词

2 个答案: